Questions about A220(formerly CS300) Control Logic

[mooooooonnn]

Hi all,

I'm gonna take simulator check for new-hired co-pilot.

The company will do simulator test in A220 for new-hired copilots. Their applicants have no experience in jets, have experiences only in single or multi engine props. (like C172, PA44)

Thus, there's no way to experience A220, cuz that model is not famous, so there's no simulator programs or place to experience.

But I found out that much differences are existing in A220. I'm trying to practice with MSFS or XPlane with A320 / B737 and A320 FTD.

There are several curiosities in control logic.

1. A220 has TOGA switch in the thrust levers, underneath the handle of it. But, in many videos taken in the cockpit of A220 while taking off, I found that pilots do not push toga button. But, I can see thrust levers are automatically set to Takeoff Thrust position. How can they do that? Is there any button that pilots should press while taking off?

2. A220 has weird control logic, speed trim. I failed to find any jets who have speed trim switch. Thus, I understood speed trims will fix the trimmed speed, so pilots have to change their speed trims only they want to change their target speed. But, you know B737, B747 or other boeing jets who have trim pilots should continuously change their trim while changing their attitude. In this part. when changing the attitude, what logic will be executed in A220? In speed trim at 210 KIAS with 0 FPM and 50%N1, in this situation, if a pilot commands back pressure on sidestick without changing thrust, airplane will decelerate. In turn, if a pilot returns his sidestick to neutral position, the airplane pitches down by speed trim system? Thus, if a pilot wants to climb, he should command back pressure on sidestick plus increase thrust?

Question 2 is the hardest part to understand ;(

Thanks for answering.

[FLX/MCT]

Hi

1. The A/T is armed with the A/T button on the FCP usually at some point during the lineup. In this armed condition, once you advance the thrust levers far enough forward the A/T becomes active and engages in "Thrust" mode and sets the proper TO thrust. So no need to push the TO/GA button at the start of the takeoff roll.

2. Thirst think about a conventional aircraft - they also show some kind of natural speed (more precisely AOA) stability. Assuming stable conditions the aircraft will eventually return to it's previous speed / AOA (in a more or less pronounced phugoid motion) after a control input without any trim adjustment.
Speed trim tries to imitate this behaviour by generating artificial feel for a fly by wire aircraft around the pitch axis, and also allowing some tactile feedback for the (mis)trim condition. This concept is also used on Boeing FBW models.

From a practical point of view, with a speed trim system you ONLY trim for desired changes in your airspeed - the control laws take care of all of the rest (e.g. thrust changes, configuration changes).

Your conclusion is correct :) To start a climb you apply some backpressure and simultaneously increase thrust - you can go hands off stick and it will climb nicely at 210 kt.
The A220 shows you a trim speed bug (cyan triangle) on the speedtape, which you adjust by pushing the trim switches on the sidestick - it is essential to keep them always as close to your target speed as possible - during speed changes apply small but regular trim inputs.
Sounds complicated on the paper but it is a really easy to handle and responsive aeroplane and can be flown really precisely.

All the best for your assessment!

[mooooooonnn]

Hi

1. The A/T is armed with the A/T button on the FCP usually at some point during the lineup. In this armed condition, once you advance the thrust levers far enough forward the A/T becomes active and engages in "Thrust" mode and sets the proper TO thrust. So no need to push the TO/GA button at the start of the takeoff roll.

2. Thirst think about a conventional aircraft - they also show some kind of natural speed (more precisely AOA) stability. Assuming stable conditions the aircraft will eventually return to it's previous speed / AOA (in a more or less pronounced phugoid motion) after a control input without any trim adjustment.
Speed trim tries to imitate this behaviour by generating artificial feel for a fly by wire aircraft around the pitch axis, and also allowing some tactile feedback for the (mis)trim condition. This concept is also used on Boeing FBW models.

From a practical point of view, with a speed trim system you ONLY trim for desired changes in your airspeed - the control laws take care of all of the rest (e.g. thrust changes, configuration changes).

Your conclusion is correct :) To start a climb you apply some backpressure and simultaneously increase thrust - you can go hands off stick and it will climb nicely at 210 kt.
The A220 shows you a trim speed bug (cyan triangle) on the speedtape, which you adjust by pushing the trim switches on the sidestick - it is essential to keep them always as close to your target speed as possible - during speed changes apply small but regular trim inputs.
Sounds complicated on the paper but it is a really easy to handle and responsive aeroplane and can be flown really precisely.

All the best for your assessment!

Wow! thanks for detailed answer. I'm glad to get your answer.
Have a nice day, and always safe flight! Thank you again.

[PPRuNeUser0202]

As FLX/MCT explained, the TO thrust is set automatically once the throttle levers are advanced by more than 23 degrees (if I remember correctly). In practice, you will enter your calculated thrust setting in the FMS (either derate or flex), arm the A/T before TO, advance the thrust levers manually to about 55% N1 to stabilise the engines, then push them forward a notch and the thrust levers will continue moving forward on their own to reach the desired N1 target.

For the speed trim, think of it like when you were flying your SEP, and your instructor telling you that you have to trim for a certain airspeed, not a pitch angle. Pitch and power always go in pair, resulting in an airspeed. The logic is more or less the same on the speed trim of the 220.
For instance in a SEP, to maintain Vy in your initial climb at full power, you will need a given pitch up angle. If you want to slow down, you have to pitch more up, if you want to accelerate you have to pitch down. With a conventional trim, you would maintain a pitch angle giving you Vy, and then trim until you don't have to pull on the stick anymore.
In a speed trim the FBW computers apply more or less the same logic. By for instance, you want to climb at 250kt. By pllacing the speed trim at 250, you basically tell the aircraft: I want to climb at speed 250, with this climb thrust. So if you are currently at 230kt, moving the speed trim to 250kt, will lower the nose. Moving the speed trim to 210 will pitch the nose up.
If you fly it fully manually with no A/T and no AP, then it works a little bit more like a conventional trim. If from level flight, you want to climb for example and only increase the thrust without touching the speed trim, the plane will want to keep the current trimmed speed. But with more thrust, to do that the nose will have to go up.

Good luck in the sim!